Polymer clad fiber for evanescent coupling

ABSTRACT

A fiber to waveguide coupler is provided that includes an optical fiber having a core and a cladding. The cladding includes an inner cladding and an outer cladding with a polymer. At least one of the core and inner cladding defines a substantially flat surface parallel with an axis of the optical fiber. The optical fiber defines a stripped portion substantially free of outer cladding configured to expose the at least one substantially flat surface of the core or inner cladding. A waveguide is configured to be evanescently coupled with the exposed at least one substantially flat surface of the core or inner cladding.

This application claims the benefit of priority under 35 U.S.C. § 119 ofU.S. Provisional Application Ser. No. 62/279,987 filed on Jan. 18, 2016the content of which is relied upon and incorporated herein by referencein its entirety.

BACKGROUND

The present disclosure generally relates to methods and apparatus forevanescently coupling, and more particularly, relates to the strippingof an optical fiber to facilitate evanescent coupling.

Conventional photonic integrated circuits typically utilize both asilicon waveguide and a polymer waveguide which are evanescently coupledon the circuit. An optical fiber is then coupled to the polymerwaveguide for providing optical signals to or from the photonic circuit.The use of the polymer waveguide on the photonic chip may lead tocoupling losses which may deteriorate the optical signal. For example,optical attenuation in the polymer waveguide may lead to a loss of about0.5 dB and coupling between the polymer waveguide and the optical fibermay result in an additional 1 dB of loss. Various additional methods ofcoupling the fiber to the circuit may decrease the signal loss, butgenerally will increase the fabrication complexity and cost of the fiberand/or the circuit, or decrease the bandwidth or channels. Additionally,coupling fibers together may lead to signal loss. Accordingly, a newmanner of transmitting optical signals between optical fibers and/orphotonic circuits is desirable.

SUMMARY

According to one aspect of the present disclosure, a fiber to waveguidecoupler is provided that includes an optical fiber having a core and acladding. The cladding includes an inner cladding and an outer claddingwith a polymer. At least one of the core and inner cladding defines asubstantially flat surface parallel with an axis of the optical fiber.The optical fiber defines a stripped portion substantially free of outercladding configured to expose the at least one substantially flatsurface of the core or inner cladding. A waveguide is configured to beevanescently coupled with the core through the exposed at least onesubstantially flat surface of the core or inner cladding.

According to another aspect of the present disclosure, a method ofevanescent coupling is provided that includes the steps: providing anoptical fiber having a core, an inner cladding and an outer cladding;providing a photonic integrated circuit comprising a waveguidepositioned within a slot; stripping a portion of the outer cladding toexpose at least a portion of the substantially flat surface; andpositioning the stripped portion of the optical fiber within the slotsuch that the substantially flat surface is proximate the waveguide andthe core is evanescently coupled with the waveguide.

According to yet another aspect of the present disclosure, a method ofevanescently coupling is provided that includes the steps of providingan optical fiber having a core and a cladding which includes a polymericmaterial; preferentially stripping a portion of the polymeric materialof the cladding from the optical fiber using a laser; providing awaveguide; and positioning the core of the optical fiber sufficientlyclose to the wave guide to evanescently couple the core of the opticalfiber to the waveguide.

According to yet another aspect of the present disclosure, an opticalfiber is provided which includes a glass core and a cladding. Thecladding includes an inner glass cladding and an outer cladding having apolymer. The cladding defines a substantially flat surface parallel withan axis of the optical fiber offset from the core by less than about 10μm.

Additional features and advantages will be set forth in the detaileddescription which follows, and, in part, will be readily apparent tothose skilled in the art from that description or recognized bypracticing the embodiments as described herein, including the detaileddescription which follows the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary and are intendedto provide an overview or framework to understanding the nature andcharacter of the claims. The accompanying drawings are included toprovide a further understanding, and are incorporated in and constitutea part of this specification. The drawings illustrate one or moreembodiments, and together with the description serve to explainprinciples and operation of the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is cross-sectional view of an optical fiber evanescently couplingwith a photonic integrated circuit, according to one embodiment;

FIG. 2A is an enlarged cross-sectional view of an optical fiber,according to one embodiment;

FIG. 2B is an enlarged cross-sectional view of an optical fiber,according to one embodiment;

FIG. 3A is an enlarged cross-sectional view of an optical fiber,according to one embodiment;

FIG. 3B is an enlarged cross-sectional view of an optical fiber,according to one embodiment;

FIG. 3C is an enlarged cross-sectional view of an optical fiber,according to one embodiment;

FIG. 4A is an exemplary method of stripping a cladding from a core of anoptical fiber, according to one embodiment;

FIG. 4B is an exemplary method of stripping a cladding from a core of anoptical fiber, according to one embodiment;

FIG. 4C is a perspective view of a stripped portion of an optical fiber,according to one embodiment;

FIG. 5 is an exemplary method of coupling an optical fiber to a photonicintegrated circuit, according to one embodiment;

FIG. 6 is an exemplary method of positioning an optical fiber to aphotonic integrated circuit, according to one embodiment; and

FIG. 7 is an exemplary method of positioning an optical fiber to asecond optical fiber, according to one embodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to the present embodiments,examples of which are illustrated in the accompanying drawings. Wheneverpossible, the same reference numerals will be used throughout thedrawings to refer to the same or like parts.

For purposes of description herein, the terms “upper,” “lower,” “right,”“left,” “rear,” “front,” “vertical,” “horizontal,” and derivativesthereof, shall relate to the disclosure as oriented in FIG. 1, unlessstated otherwise. However, it is to be understood that the disclosuremay assume various alternative orientations, except where expresslyspecified to the contrary. It is also to be understood that the specificdevices and processes illustrated in the attached drawings, anddescribed in the following specification, are simply exemplaryembodiments of the inventive concepts defined in the appended claims.Hence, specific dimensions and other physical characteristics relatingto the embodiments disclosed herein are not to be considered as limitingunless the claims expressly state otherwise. Additionally, embodimentsdepicted in the figures may not be to scale or may incorporate featuresof more than one embodiment.

As used herein, the term “and/or,” when used in a list of two or moreitems, means that any one of the listed items can be employed by itself,or any combination of two or more of the listed items can be employed.For example, if a composition is described as containing components A,B, and/or C, the composition can contain A alone; B alone; C alone; Aand B in combination; A and C in combination; B and C in combination; orA, B, and C in combination.

Referring to FIG. 1, depicted is an optical fiber 10 coupled to aphotonic integrated circuit 14. The optical fiber 10 includes a glassportion 16 and a polymeric portion 20. The glass portion 16 may includea core 18 and an inner cladding 54 (FIG. 3A). The polymeric portion 20may include an outer cladding 58 (FIG. 3A) positioned around the glassportion 16. The inner cladding 54 and the outer cladding 58 maycooperate to form a cladding 22 disposed around the core 18. The glassportion 16 may define one or more substantially flat surfaces, such as acore surface 26 (FIG. 3A) or a cladding surface 62 (FIG. 3A). The flatsurfaces (e.g., core surface 26 or cladding surface 62) may be parallelwith an axis of the fiber 10 and/or extend coaxially with the opticalfiber 10 for either a portion of the fiber 10 or the entire length ofthe fiber 10. The optical fiber 10 may include one or more strippedportions 28 where a portion, or all of the polymeric portion 20 (e.g.,all or part of the cladding 22), has been removed or stripped from theoptical fiber 10 such that one or more of the flat surfaces (e.g., thecore surface 26 and/or cladding surface 62) are exposed. The glass core18 may be composed of pure silica, doped silica (e.g., doped withgermanium, aluminum, and/or chlorine) and/or other optically transparentmaterials. The inner cladding 54 may be composed of pure silica, dopedsilica (e.g., fluorine and/or boron) or other optically transparentmaterials. The optical fiber 10 may be a single mode fiber or may be amulti-mode fiber. The core 18 may have a higher refractive index thanthe inner cladding 54. The core 18 may have a relative refractive indexchange, or delta, relative to the inner cladding 54 in the range ofabout 0.2% to about 3.0%, for example about 0.34%, about 0.5%, about1.0%, about 1.5%, about 2.0%, about 2.5% or about 3.0%. The core 18,inner cladding 54 and/or outer cladding 58 may be tapered. The cladding22 may be a composite (e.g., inner cladding 54 is composed of glass andthe outer cladding 58/polymeric portion 20 is composed of a polymer).The refractive indexes of the materials of the cladding 22 may have alower refractive index than the core 18. It will be understood that theoptical fiber 10, as described herein, may simply be a connection orconnector to another longer or larger optical fiber.

Referring again to FIG. 1, the photonic integrated circuit 14 includes asubstrate 30 having a buried oxide layer 34, a top oxide layer 36 and awaveguide 38. The waveguide 38 may include silicon, silicon nitride,glass, polymers, combinations thereof and/or other materials. Thesubstrate 30 may be a silicon substrate, glass substrate or othersupport structure capable of supporting and defining optical devices.The top oxide layer 36 is configured to define a slot 42 within whichthe optical fiber 10 and the waveguide 38 are positioned. The buriedoxide layer 34 may be formed at the bottom surface of the top oxidelayer 36 of the substrate 30 or be positioned on a surface of thesubstrate 30. The buried oxide layer 34 may be formed prior to selectivebonding of the top oxide layer 36 to the bulk substrate 30. Further, theburied oxide layer 34 may be formed by oxygen implanting to a desireddepth within the substrate 30. The slot 42 may be formed in the topoxide layer 36 via etching, mechanical forming, or other conventionalmethods known in the art. The slot 42 may have a depth of between about5 μm and about 200 μm, or between about 10 μm and about 125 μm, orbetween about 15 μm and about 50 μm. The slot 42 may have a width ofbetween about 5 μm and about 10 μm, or between about 50 μm and about 125μm, or between about 125 μm and about 200 μm. The slot 42 is shaped andsized to accept the stripped portion 28 of the optical fiber 10. Thewaveguide 38 may be planar and is positioned within the top oxide layer36 and within the slot 42. The waveguide 38 may be a silicon waveguide38 configured to carry an optical signal along the photonic integratedcircuit 14 to a detector or other optical circuitry located on or offthe circuit 14. The waveguide 38 may have a mode field diameter similarto that of the optical fiber 10 and may be tapered or not tapered in adirection transverse to the direction of light propagation along thelength of the waveguide 38. The waveguide 38 may be tapered, or reduced,to less than about 70%, less than about 60%, or less than about 50% ofits original width (e.g., from about 200 nm to about 120-160 nm). Dopingof the core 18 may facilitate a less narrow taper of the waveguide 38 tobe achieved. The waveguide 38 defines a waveguide surface 46 which maybe substantially flat and configured to couple with the core 18 throughthe core surface 26 and/or the cladding surface 62 of the inner cladding54.

The optical fiber 10 is configured to carry one or more optical signalsalong the core 18. The placement of the stripped portion 28 of theoptical fiber 10 within the slot 42 places the optical fiber 10 inclose, intimate, contact with the waveguide 38 such that optical signalsmay be transferred between the two. For example, the core surface 26and/or the cladding surface 62 of the stripped portion 28 aresufficiently proximate to the waveguide surface 46 of the waveguide 38in the plane of the substrate 30 for an evanescent field of lightpropagating through the optical fiber 10 to enter the waveguide 38, orvice versa. Evanescent coupling between the optical fiber 10 and thewaveguide 38 may transfer greater than about 1%, greater than about 5%,greater than about 10%, greater than about 25%, greater than about 50%,greater than about 60%, greater than about 70%, greater than about 80%,greater than about 90%, or about substantially 100% of the optical powerbetween the optical fiber 10 and the waveguide 38. The core surface 26and/or cladding surface 62 may overlap the waveguide surface 46 of thewaveguide 38 between about 10 μm and about 3000 μm to facilitateevanescent coupling. Tapering of the waveguide 38 such that theeffective index of the waveguide 38 matches that of the core 18 mayfacilitate or increase the power transfer between the optical fiber 10and the waveguide 38.

Referring now to FIGS. 2A-3C, depicted are various embodiments of theoptical fiber 10 having different configurations of the glass portion 16and the polymeric portion 20. In order for the core surface 26 of thecore 18 and/or the cladding surface 62 to get close enough to thewaveguide surface 46 (FIG. 1) of the waveguide 38 (FIG. 1) to facilitateevanescent coupling, the core 18 and inner cladding 54 may take avariety of cross-sectional shapes configured to expose the core surface26 and/or cladding surface 62 once the polymeric portion 20 has beenstripped off. The cross-sectional shape of the core 18 may be square(FIGS. 2A and 3A), D-shaped (FIG. 2B), round or circular (FIG. 3B), atruncated circle (FIG. 3C), triangular, rectangular, truncatedtriangular or other polygons configured to define the core surface 26which extends along a length of the core 18. The cross-sectional shapeof the core 18 may extend the entire length of the core 18 or may onlyextend for a portion of the core 18 (e.g., the area intended to be thestripped portion 28 (FIG. 1)). The cross-sectional shape of the core 18and/or the glass portion 16 may be developed in the preform stage of theoptical fiber 10, and the core 18 and/or the glass portion 16 of thepreform may have specific geometries (e.g., corners removed) applied tomaintain the core surfaces 26 of the core 18 during production of theoptical fiber 10. The core 18 may have a diameter, largest straight linedimension or width of the flat surface 26 of about 6 μm, about 7 μm,about 8 μm, about 9 μm, about 10 μm, about 11 μm, about 12 μm, about 13μm, about 14 μm or about 50 μm. The diameter of the core 18 may be largeenough such that the mode field diameter of the core 18 is approximatelythat of a single mode fiber. The diameter of the core 18 may also beconfigured for specific design purposes to have a large or small modefield diameter. The diameter of the optical fiber 10 may be greater thanabout 80 μm, greater than about 100 μm, greater than about 110 μm,greater than about 120 μm, greater than about 130 μm or greater thanabout 140 μm. In a specific example, the diameter of the optical fiber10 may be about 125 μm.

Referring now to FIGS. 3A-3C, as explained above, the cladding 22 of theoptical fiber 10 may be divided into the inner cladding 54 and the outercladding 58 (e.g., polymeric portion 20). The outer cladding 58 mayinclude a glass, a polymeric material or composites thereof. Thepolymeric material may include high density polyethylene, low densitypolyethylene, polystyrene, polymethylmethacrylate, nylon, acrylate,silicone, silicone based materials, fluorinated acrylates, polyimide,ethylene tetrafluoroethylene, fluoroacrylate, fluoromethacrylate andcombinations thereof. The polymeric material may be opticallytransparent. The polymeric portion 20 may have a diameter ranging frombetween about 40 μm and about 500 μm, between about 80 μm and about 250μm or between about 100 μm and 150 μm. In a specific example, thepolymeric portion 20 is sufficiently thick that the core 18 and thecladding 22 have a diameter of about 125 μm. A polymeric jacket may bedisposed around the outer cladding 58. The polymeric jacket may have alower optical transparency than the outer cladding 58. The polymericportion 20 may have a refractive index only slightly above or below thatof the inner cladding 54. The inner cladding 54 may include a glass ormaterial other than polymers such that the cladding 22 is a compositecladding 22. The inner cladding 54 may have a general square, circular,triangular, polygonal or D-shape similar to that of the core 18 of FIG.2B. The diameter, or longest cross-sectional length, of the innercladding 54 may range from between about 15 μm to about 170 μm, fromabout 20 μm to about 150 μm, from about 30 μm to about 140 μm, fromabout 40 μm to about 125 μm or from about 50 μm to about 115 μm. Theinner cladding 54 may have a refractive index the same or substantiallysimilar to that of the outer cladding 58. In some embodiments, the outercladding 58 may have a lower refractive index than the inner cladding 54(e.g., to prevent tunneling loss). In the depicted embodiments, theD-shape of the inner cladding 54 defines the cladding surface 62 whichis configured to intimately couple with the waveguide surface 46(FIG. 1) of the waveguide 38 (FIG. 1). It will be understood that inembodiments not utilizing the inner cladding 54, the cladding 22 orouter cladding 58 may define the cladding surface 62. The claddingsurface 62 may be offset from the core surface 26 of the core 18 (FIGS.3A and 3B) or may be in line, or aligned with, the core surface 26 (FIG.3C). The cladding surface 62 may be offset from the core surface 26 ofthe core 18 by between about 0.1 μm and about 10 μm, or between about 1μm and about 5 μm. If very strong coupling between the optical fiber 10and the waveguide 38 is desired, the example depicted in FIG. 3C may beused. The outer cladding 58 may have a diameter of between about 25 μmand about 500 μm, or between about 50 μm and about 250 μm or betweenabout 100 μm and about 125 μm.

Referring now to FIGS. 4A-4C, the polymeric portion 20 may be removedfrom the optical fiber 10 to form the stripped portion 28 via a varietyof methods. In a first example, the polymeric portion 20 may be strippedfrom the core 18 using one or more laser beams 66. For example, thelaser beams 66 may emanate from a gas laser (e.g., CO₂, Ar, HeNe, HeAgand/or NeCu), a chemical laser, an excimer laser, a solid state laserand/or other sources of laser beams 66. In the depicted examples, one ormore laser beams 66 may be directed at the polymeric portion 20. Thedifference in optical absorption and/or evaporation temperature betweenthe material of the polymeric portion 20 and the glass portion 16 (e.g.,core 18 and inner cladding 54 (FIG. 3A)) permits selective orpreferential removal of the polymeric portion 20 or outer claddingmaterial 58 (FIG. 3A). The laser beams 66 may be applied to thepolymeric portion 20 such that the optical fiber 10 has a profiled shapewhich may aid in alignment and positioning of the fiber 10 within theslot 42 (FIG. 1) and coupling to the waveguide 38 (FIG. 1). In thedepicted example of FIG. 4A, a single laser beam 66 has been applied tothe optical fiber 10 to remove the polymeric portion 20 such that thepolymeric portion 20 defines a polymeric surface 20 a which is alignedwith the core surface 26 of the core 18. In the depicted example of FIG.4B, one or more laser beams 66 may be applied to the polymeric portion20 such that the polymeric portion 20 is removed from the core surface26 of the core 18 and the polymeric portion 20 of the optical fiber 10is profiled in a V-shape. The polymeric portion 20 may be profiled suchthat the polymeric surface 20 a forms an angle between about 1° andabout 60°, or between about 20° and about 55°, relative to the coresurface 26. In a specific example, the angle of the polymeric surface 20a may be about 45°. In another embodiment, a chemical etchant (e.g.,methylene chloride) may be applied to the optical fiber 10 which isconfigured to preferentially remove the polymeric portion 20 withoutdamaging the core 18. In yet another embodiment, the polymeric portion20 may be thermally stripped from the core 18 using a thermal strippingtool. The thermal stripper may melt or soften the polymeric portion 20without softening the core 18 such that the polymeric portion 20 may beremoved without damaging the core 18 or inner cladding 54. In yetanother embodiment, the polymeric portion 20 may be mechanically removedfrom the core 18 or inner cladding 45 via grinding, slicing, stripping,a miller stripper and/or other acceptable methods.

During the stripping of the polymeric portion 20, a visual alignmentsystem may be utilized. An exemplary alignment system may include arotational stage on which the optical fiber 10 would be placed. An endface of the optical fiber 10 could be imaged using a camera and thenrotated such that the fiber 10 is aligned with the stripping system thatis used. In embodiments utilizing the inner cladding 54, the claddingsurface 62 may be polished post stripping to ease coupling of theoptical fiber 10 to the waveguide 38.

Referring now to FIG. 4C, the polymeric portion 20 of the optical fiber10 may be stripped not only to form a cross-sectional profile, but thepolymeric portion 20 may be stripped to transition between the strippedportion 28 and an unstripped portion (e.g., the remainder of the opticalfiber 10). In the depicted embodiment, the polymeric portion 20 may bestripped to form a transition portion 70 which transitions the opticalfiber 10 from the stripped portion 28 to the unstripped polymericportion 20. In various embodiments, the transition portion 70 may beconfigured to transition the optical fiber 10 to the stripped portion 28adiabatically (e.g., the rate of change of the effective index of theguided optical wave may be smaller than the wavelength of the light inthe core 18) such that optical loss is minimized through the transitionportion 70. In the depicted example, the transition portion 70 isangled, but may take a variety of shapes configured to transition theoptical fiber 10 between the stripped portion 28 and the unstrippedpolymeric portion 20.

Referring now to FIGS. 5 and 6, once the polymeric portion 20 has beenstripped from the optical fiber 10 to form the stripped portion 28 (FIG.1), the stripped portion 28 may be positioned within the slot 42. Asexplained above, positioning of the stripped portion 28 of the opticalfiber 10 within the slot 42 may evanescently couple the core 18 of theoptical fiber 10 to the waveguide 38 of the photonic integrated circuit14. It will be understood that a high index coupling agent (e.g., anepoxy) may be disposed between the core 18 and/or inner cladding 54(FIG. 1) and the waveguide 38 to counter any thermal movement and toenable more efficient coupling.

Referring now to FIG. 5, as explained above, the optical fiber 10 may beprofiled in the stripped portion 28 such that the polymeric portion 20forms a general V-shape. Such a V-shape may be advantageous in providingthe optical fiber 10 with a “self-centering” attribute allowing for easycoupling of the core 18 to the waveguide 38. The V-shape of thepolymeric portion 20 permits the optical fiber 10 to contact the topoxide layer 36 during insertion while guiding the core surface 26 of thecore 18 and/or cladding surface 62 toward the waveguide surface 46 ofthe waveguide 38. It will be understood that the slot 42 may also have ageneral V-shape to aid in insertion of the optical fiber 10.

Referring now to FIG. 6, in the depicted example, the polymeric portion20 has been removed from a portion of three of the flat surfaces 26 ofthe core 18. In such an embodiment, the slot 42 may be dimensioned onlyslightly larger (e.g., greater than about 0.1 μm, greater than about 0.5μm, greater than about 1.0 μm or greater than about 2 μm) than the core18 such that the core 18 may couple with the slot 42 and the waveguide38. The polymeric surface 20 a of the polymeric portion 20 may contactthe top oxide layer 36 external to the slot 42 and aid in securing ofthe optical fiber 10 to the photonic integrate circuit 14. In thedepicted example, only the core 18 (e.g., or core 18 and inner cladding54 in associated embodiments) is within the slot 42 and the polymericportion 20/cladding 22 is outside of the slot 42. Put another way, thecladding 22 is not in the slot 42.

Referring now to FIG. 7, the optical fiber 10 may be evanescentlycoupled to a second optical fiber 10 a having a second glass portion 16a and a second polymeric portion 20 b. The second polymeric 20 b may bestripped in a substantially similar manner to that described inconnection with the polymeric portion 20 above such that a secondstriped portion 28 a is formed where a portion of a second cladding 22a, or second polymeric portion 20 b, is removed. By positioning thestripped portion 28 of the optical fiber 10 and the second strippedportion 28 a of the second optical fiber 10 a sufficiently close, thecore 18 of the optical fiber 10 may be evanescently coupled with asecond core 18 a of the second optical fiber 10 a similarly to thatexplained above between the waveguide 38 and the optical fiber 10. Oneor more coupling agents, clamps or other devices may be used to securethe optical fiber 10 to the second optical fiber 10 a.

Use of the present disclosure may offer several advantages over existingtechniques for coupling optical fibers 10 to photonic integratedcircuits 14 and to other optical fibers. First, evanescent couplingallows for in plane light output, broadband optical performance, and lowoptical loss. In plane light output where the light stays in the sameplane as the optical fiber 10 and the photonic integrated circuit 14means there may not be a need for an additional photonic turn and thepackaging may be compact. Use of evanescent coupling allows forpotentially no loss of optical power. Further, use of the polymericportion 20 having the stripped portion 28 may allow for quick, easy andaccurate placement of the optical fiber 10 within the photonicintegrated circuit 14 or to another optical fiber. The profiled shapesdisclosed herein allow for the macro-nature of the optical fiber 10 tobe retained (e.g., the cladding 22 and/or polymeric portion 20) whileproviding structures (e.g., the V-shape of the optical fiber 10) thatfacilitate micro-precision placement (e.g., the core surface 26 or thecladding surface 62 proximate the waveguide surface 46 of the waveguide38). Additionally, by leveraging the highly accurate fiber drawingprocess, the coupling loss of the optical fiber 10 to the waveguide 38due to the highly uniform core surface 26 and cladding surface 62 may beminimal and highly repeatable.

While the embodiments disclosed herein have been set forth for thepurpose of illustration, the foregoing description should not be deemedto be a limitation on the scope of the disclosure or the appendedclaims. It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the claims.

It will be understood by one having ordinary skill in the art thatconstruction of the described disclosure and other components is notlimited to any specific material. Other exemplary embodiments of thedisclosure disclosed herein may be formed from a wide variety ofmaterials, unless described otherwise herein. In this specification andthe amended claims, the singular forms “a,” “an,” and “the” includeplural reference unless the context clearly dictates otherwise.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit, unlessthe context clearly dictates otherwise between the upper and lower limitof that range, and any other stated or intervening value in that statedrange, is encompassed within the disclosure. The upper and lower limitsof these smaller ranges may independently be included in the smallerranges, and are also encompassed within the disclosure, subject to anyspecifically excluded limit in the stated range. Where the stated rangeincludes one or both of the limits, ranges excluding either or both ofthose included limits are also included in the disclosure.

For purposes of this disclosure, the term “coupled” (in all of itsforms: couple, coupling, coupled, etc.) generally means the joining oftwo components (optical, electrical or mechanical) directly orindirectly to one another. Such joining may be stationary in nature ormovable in nature. Such joining may be achieved with the two components(optical, electrical or mechanical) and any additional intermediatemembers being integrally formed as a single unitary body with oneanother or with the two components. Such joining may be permanent innature, or may be removable or releasable in nature, unless otherwisestated. It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the claims.

For the purposes of describing and defining the present teachings, it isnoted that the terms “substantially” and “approximately” are utilizedherein to represent the inherent degree of uncertainty that may beattributed to any quantitative comparison, value, measurement, or otherrepresentation. The term “substantially” and “approximately” are alsoutilized herein to represent the degree by which a quantitativerepresentation may vary from a stated reference without resulting in achange in the basic function of the subject matter at issue.

It is to be understood that variations and modifications can be made onthe aforementioned structure without departing from the concepts of thepresent invention, and further it is to be understood that such conceptsare intended to be covered by the following claims unless these claimsby their language expressly state otherwise.

What is claimed is:
 1. A fiber to waveguide coupler comprising: anoptical fiber having a core and a cladding, the cladding comprising aninner cladding and an outer cladding comprising a polymer, at least oneof the core and inner cladding having a substantially flat surfaceparallel with an axis of the optical fiber, the flat surface extendingalong the entire length of the optical fiber, wherein the optical fiberincludes a stripped portion substantially free of the outer claddingconfigured to expose at least a portion of the at least onesubstantially flat surface of the core or inner cladding, and wherein atransition portion between the stripped portion and the outer claddingis adiabatic; and a waveguide configured to evanescently couple with thefiber through the exposed at least one substantially flat surface of thecore or inner cladding, wherein the stripped portion of the opticalfiber and the waveguide extend into and couple within a slot.
 2. Thefiber to waveguide coupler of claim 1, wherein the waveguide is a planarwaveguide positioned on a photonic integrated circuit.
 3. The fiber towaveguide coupler of claim 1, wherein the core and the inner claddingeach include a substantially flat surface.
 4. The fiber to waveguidecoupler of claim 3, wherein the substantially flat surface of the coreand the substantially flat surface of the inner cladding are offset. 5.The fiber to waveguide coupler of claim 3, wherein the substantiallyflat surface of the core and the substantially flat surface of the innercladding are aligned with one another.
 6. The fiber to waveguide couplerof claim 1, wherein only the inner cladding includes a substantiallyflat surface.
 7. The fiber to waveguide coupler of claim 1, wherein thepolymer is at least one of a fluorinated acrylate and a silicone.
 8. Amethod of evanescent coupling comprising the steps: providing an opticalfiber having a core, an inner cladding and an outer cladding, the corecomprising glass, wherein the inner cladding defines a substantiallyflat surface extending along the entire length of the optical fiber andthe outer cladding comprises a polymeric material; providing a photonicintegrated circuit comprising a waveguide positioned within a slot;stripping a portion of the outer cladding to expose at least a portionof the substantially flat surface; and positioning the stripped portionof the optical fiber within the slot such that the exposed substantiallyflat surface is proximate the waveguide and the core is evanescentlycoupled with the waveguide.
 9. The method of claim 8, wherein thewaveguide is tapered in a direction perpendicular to a direction oflight propagation through the waveguide.
 10. The method of claim 8,wherein the slot of the photonic integrated circuit is defined by anoxide and the stripping of the outer cladding creates a V-shaped profileto the optical fiber.
 11. The method of claim 10, wherein the innercladding has a higher refractive index than the outer cladding.
 12. Themethod of claim 8, wherein only the core is positioned within the slot.13. The method of claim 8, wherein a transition between the strippedportion and the outer cladding is adiabatic.
 14. An optical fibercomprising: a glass core; and a cladding, the cladding comprising aninner glass cladding and an outer cladding comprising a polymer, whereinthe cladding includes a substantially flat surface parallel to an axisof the optical fiber, the substantially flat surface extending along theentire length of the optical fiber and being offset from the core byless than about 10 μm.
 15. The optical fiber of claim 14, wherein theouter cladding has a refractive index the same or lower than the innercladding.
 16. The optical fiber of claim 14 further comprising: astripped portion where the outer cladding is removed to expose a portionof the substantially flat surface.
 17. The optical fiber of claim 16,wherein a cross-sectional shape of the optical fiber at the strippedportion is substantially a D-shape.
 18. The optical fiber of claim 16,wherein a cross-sectional shape of the optical fiber at the strippedportion is substantially a V-shape.
 19. The optical fiber of claim 14,wherein the polymer is at least one of a fluorinated acrylate and asilicone.
 20. The optical fiber of claim 19, wherein the outer claddinghas a diameter between about 100 μm and about 150 μm.
 21. The opticalfiber of claim 14, wherein the outer cladding comprises a transitionportion between the stripped portion and an unstripped portion of theoptical fiber, and wherein the transition portion is configured totransition adiabatically from the unstripped portion to the strippedportion.
 22. The optical fiber of claim 1, wherein the inner claddingcomprises glass.
 23. The fiber to waveguide coupler of claim 1, whereinthe waveguide is tapered in a direction perpendicular to a direction oflight propagation through the waveguide.
 24. The fiber to waveguidecoupler of claim 1, wherein the outer cladding is tapered.
 25. The fiberto waveguide coupler of claim 1, wherein the outer cladding has a lowerrefractive index than the inner cladding.
 26. The optical fiber of claim14, wherein the outer cladding has a lower refractive index than theinner cladding.